Nitrogen incorporation into boron-doped graphite and formation of B-N bonding

Carbon materials having different levels of boron doping were prepared from a mixture of coke and boron carbide at temperatures between 2000 and 2800 degrees C. The XRD measurements showed that crystallites grow with an incre ase of boron concentration during the preparation and there is a limited co ncentration of boron in solid solution. Unexpectedly, XPS measurements reve aled the increase of N 1s peak intensity with the increase of B 1s peak int ensity. The binding energies of these peaks suggested the formation of B-N type bond, though it was not observed by XRD. It implies that the doped bor on gives rise to the incorporation of nitrogen in the surface layer of carb on materials. A possible source of nitrogen is air occluded in raw material s during packing into graphite crucibles. Such small amounts of nitrogen mu st be taken into account with boron-doped carbon materials at high temperat ures. (C) 1999 Elsevier Science Ltd. All rights reserved.